Electrocution of cattle - A RECI perspective

Hugh Scanlan

"Electrocution -A horrific scene" - This heading in a recent issue of the Farmers Journal caught the attention of an RECI inspector.

The article described how a farmer in Borris, Co Carlow came out into his yard on a Monday morning and found six dead bullocks, one more dying and a further seven down.

The article went on to explain how the accident had occurred. It stated that the re-wired dwelling house and a new slatted shed had passed all the standards for RECI approval.

RECI (The Register of Electrical Contractors of Ireland) is a regulatory body for the electrical contracting industry and its role is to ensure that RECI registered contractors carry out their electrical installation work in accordance with the National Wiring Rules which are published by the Electro-Technical Council of Ireland.

In order to fully understand how the electrical fault occurred, RECI asked to be allowed to carry out their own inspection of the installation.

RECI were very concerned that the description of the reasons for the electrocution given in the article might lead other farmers to believe that the electrical bonding stipulated in the National Rules for Electrical Installations (Wiring Rules) is not necessary or is a potential hazard.

Importance of equipotential bonding

Because cattle are even more sensitive to electrical shock than humans, it is crucially important to minimise voltage differences which can occur between metal components and earth in locations such as milking parlours and livestock sheds.

The way this is done is through equipotential bonding. What this means is that every part of the exposed metal work is electrically bonded together and bonded to earth so that there are no potentially dangerous voltage differences to cause electric shock.

In order to prevent dangerous touch voltages, the earthing and bonding must be adequately designed and installed.

It should be noted that apart from the danger to life, quite low voltages can reduce milk production and cause mastitis in cattle.

Equipotential bonding in a milking parlour

In order to reduce the possibility of stray voltages to a minimum, it is recommended that a metal equipotential bonding grid should be located in the floor of milking parlours.

The connections from this floor grid to the main bond structure of the milking parlour should be at least duplicated - connections being made at opposite ends of the grid.

Whenever possible the milking parlour furniture should be connected to the floor grid when they are being installed in the floor. This would be an addition to the normal bonding connections in the milking parlour.

In new installations the standard concrete reinforcing mat may be used for this purpose. In an existing milking parlour the bonding grid may be located in a screed laid on the existing floor: or it may be provided by inserting bonding conductors in slots cut in the floors.

Equipotential bonding is an essential safety measure specified in order to create an earthed equipotential zone in which exposed metallic parts of electrical equipment, metallic services such as water pipes and structural steelwork etc are connected together and to the main earthing terminal of the electrical installation.

This ensures that, provided all aspects of the entire electrical installation are otherwise sound, a hazard associated with dangerous touch voltages should not arise.

Equipotential Bonding is part of the Wiring Rules and is not an optional requirement as might be inferred from the article.

Cause of accident

RECI inspector, David Breen, visited the farm in Borris. He did a detailed check of the visible parts of the installation and carried out electrical testing.

The electrical installation in the slatted shed was found to be in order and in compliance with the National Wiring Rules.

However various items of existing electrical work at other parts of the farm (supplied from the same power source at the dwelling house) were seriously inadequate in both design and construction.

RECI were not involved in the initial investigation into the electrocution of cattle at this farm and since our inspection took place some weeks after the event, when suspect wiring to other parts of the farm was no longer in service, it was not possible to come to a definitive conclusion on the cause of the problem.

Any of a number of issues may have contributed to the transfer of the effects of a fault from another part of the farm to the slatted shed.

These include a damaged buried cable to an outhouse which was inadequately protected, dampness at a connection not contained in a suitably I.P. rated enclosure, incorrectly rated fuse in an existing Distribution Board.

Likewise any significant deficiency in the overall earthing arrangement of the entire installation, at the time of the accident, would have reduced the capacity of any particular part of the installation to clear fault or leakage currents as required.

It must, therefore be emphasised that all electrical installation work associated with farming undertakings should be verified as being of suitable design and in compliance with the National Wiring Rules.

It is also most important to ensure that if an electrical installation is required to be neutralised by ESB, which is the norm, that this is done.

In the case of the farm in Borris, the electrical installation in the dwelling house and the new slatted shed complied with the Wiring Rules but, unfortunately, the old wiring in the rest of the farm did not, which led to the electrocution of the cattle.

RECI standards specify that, when adding onto an existing installation, the contractor must check that the earthing system on this installation is working satisfactorily.

At this stage, it can only be assumed that everything was OK on the day the test was carried out and that there was subsequent deterioration, most likely in the underground cable, giving rise to the problem.

The lesson to be learned, from this case, is that it is always better to rewire the whole unit rather than merely the new section that is being added on.

The do's and don'ts to ensure your safety on the farm

RECI strongly advise farmers to be conscious of the potential dangers of electrical installations on farms. It is recommended that a registered contractor is engaged to carry out any extensions or renovations. Farmers should not do this themselves unless they are very satisfied that they understand the Wiring Rules and electrical installations.

The following do's and don't's should be carefully observed:-

Dos

• Do ensure everyone on the farm is conscious of the need to be careful when using electricity:
• Do have regular inspection and maintenance of your electrical installation carried out by a registered contractor.
• Do contact a registered electrical contractor, when in doubt about the safety of equipment or an installation.
• Do check portable electrical tools, particularly their flexible leads and plugs, for defects before use.
• Do switch off, lock off or unplug equipment before starting any maintenance or repair job.
• Do ensure that electrical equipment and fittings are designed for farm use in accordance with the Wiring Rules.

Don'ts

• Don't use domestic -type sockets, plugs, switches etc. in farm buildings.
• Don't continue to use faulty equipment or circuits; if in any doubt switch off and call a registered electrical contractor.
• Don't extend cables or flexes by twisting wires together and taping over.
• Don't route wiring or trailing leads where they can be damaged, eg through corrugated sheeting.
• Don't allow trailing leads to become a permanent part of an installation.
• Don't connect any portable tools, de-horners or infra-red lamps, into lamp holders or through lighting circuits.